1. Field of the Invention
The present invention relates to biomass processing. It has particular, but not exclusive, application in the field of pyrolysis and/or gasification of algae biomass.
2. Related Art
Biomass pyrolysis is the thermal decomposition of biomass (e.g. plant material such as wood, wood bark, grasses, straw and algae) substantially in the absence of oxygen. Biomass is typically a mixture of hemicellulose, cellulose, lignin and small amounts of other organics.
The heating temperature and vapour residence times determine the proportion of gas, liquid and char produced by pyrolysis. For example, fast pyrolysis operates at moderate temperatures of 350 to 500° C. and short vapour residence times of less than two seconds to yield up to 75 wt. % liquid product on dry feed basis (A. V. Bridgwater, D. Meier, D. Radlein, “An overview of fast pyrolysis of biomass”, Organic Geochemistry, 1999, 30, 1479-1493, incorporated herein by reference).
Dried algae mass is a useful source of biomass. Algae has a high biomass production rate per unit of hectare. Typically, 1.9 tons of dry algal biomass may be produced per day per hectare compared to 60 to 70 tons of grass per hectare per year (www.algaelink.com, accessed 8 May 2008).
Algae may be grown in ponds or bioreactors. To achieve fast growth rates, algae should be provided with carbon dioxide at a higher concentration than atmospheric carbon dioxide. Light and carbon dioxide are critical for photosynthesis, which allows the algae to grow. Nutrients are also required as rapid growth depletes any existing nutrient sources. Furthermore, for optimal growth, algae should be kept in the temperature range of 20 to 25° C.
WO 2007/144441 discloses a system of cultivating phytoplankton using solar or artificial light. The phytoplankton are harvested and useful chemical compounds are extracted.
U.S. Pat. No. 6,477,841 discloses a system for growing macroalgae in a body of water using solar energy. The macroalgae are harvested and combusted in a fluidized bed combustion chamber in an artificial atmosphere of oxygen and carbon dioxide.